(a) Field of the Invention
The present invention relates to a device and method for controlling a shift of a vehicle, and more particularly, to a device and method for controlling a shift of a vehicle based on a degree of a road gradient during coasting.
(b) Description of the Related Art
Generally, when the driver releases an accelerator pedal while driving a vehicle, the vehicle is coasting by the inertia. Typically, when a vehicle speed and an engine speed exceed certain values, the engine control apparatus cuts off the fuel injected into the engine to improve fuel efficiency. When the fuel is cut off when the vehicle is coasting, the engine acts as a load on the driving system, the vehicle speed is rapidly decreased.
However, when the driver wants to maintain a particular speed (hereinafter, constant speed) by coasting, there is an inconvenience of requiring the accelerator pedal to be re-engaged to maintain the constant speed, and the fuel efficiency deteriorates due to re-acceleration. Accordingly, the transmission is operated to the neutral state by a manual transmission driver during the coasting, and the vehicle is driven by vehicle inertia. Further, in the case of an automatic transmission, when the coasting condition is detected, the fuel is automatically cut off without disconnecting the power to the transmission, thus causing unintentional deceleration through driving resistance.
In order to solve such a problem, a neutral control method was developed so that when the coasting condition is detected, the transmission is automatically set to neutral and when the accelerator or brake pedal are again engaged, the transmission is reengaged. However, since the conventional neutral control method performs a neutral control based on accelerator and brake operation by the driver, there is a problem of frequent releasing and engaging of the forward driving stage clutch when the driver frequently operates the accelerator and brake pedals.
Thus, when releasing and engaging of the clutch is repeated, a rattling is generated when the clutch is engaged, and the drivability is deteriorated due to the acceleration delay. In addition, in the conventional neutral control method, when the forward driving stage is returned based on a gradient of the road, it does not distinguish the return stage based on the gradient. Therefore, shifting to lower stage by operation of the accelerator pedal may be difficult after returning from neutral stage to high stage.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.